Nationally there were 353 MPs who claimed at least once for a standard-class ticket in 2015-16 but didn’t claim any first-class tickets.

Virgin train (Image: Martin Keene/PA Wire)

MPs also took a total of 1,398 business or club-class flights at the taxpayers’ expense. The total bill was £499,652.

At the same time, they took just 983 economy-class flights at £161,569.

The analysis comes in the light of Jeremy Corbyn’s ‘traingate’ affair - in which the Labour leader claimed he had to sit on the floor of a Virgin train because of overcrowding issues. Virgin disputed his account and Mr Corbyn later clarified he had been unable to find two unreserved seats together in standard compartments for him and his wife.

Mr Corbyn is among those MPs who refuse to use first class, and in any case his ‘traingate’ trip was on party business and therefore not covered by the taxpayer.

MPs are allowed to claim for first-class train travel on expenses when undertaking parliamentary business where the cost of the ticket is cheaper than the standard-class ‘open’ fare.

That is essentially the cost of a walk-on, ‘on the day’ ticket - and therefore it is often cheaper to book a first-class seat in advance. It would, however, in almost all cases be even cheaper to book a standard-class ticket in advance - leading to claims MPs are taking advantage of a loophole.